Clean the whole system, tube to duct

July 18, 2000
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The complete annual maintenance of any building is essential in the reduction of operating costs and in providing a clean, healthy environment.

Tube and duct cleaning are necessary in order to keep a building running at its peak performance. The chiller and boiler systems’ internal tubes must be scrubbed, and the hvac ductwork has to be cleaned and sanitized if necessary.

A dirty chiller or boiler is caused by the formation of deposits on the tube walls and can cost a building owner an additional $25,000 per year in utility costs.

Tube cleaning would alleviate that overage in operating costs.

“It is not uncommon to have 1/2% fouling of chiller tubes. Annual tube cleaning increases our efficiency dramatically,” said Tony Zagorini, planner and scheduler for Grubb & Ellis at the IBM plant, Poughkeepsie, NY.

Scale is mineral deposit from water that forms on the chiller’s tube wall. Soot, the residue from burned energy (oil, coal, etc.) forms on boilers. These deposits act as insulation and reduce efficiency. Annual tube cleaning helps alleviate that overage in operating costs.

Cleaning the tube

Over the years, there have been many different methods used for cleaning internal tubes.

Technicians first used a rigid steel or plastic rod with a brush attached to the end. This rod would be inserted into the tube, with the technician pushing it in and out of every tube.

It was a very slow and laborious process with marginal results because the tube would be scraped — not brushed — which left residue in the tube. Also, imagine cleaning 1,000, 10,000, or even 60,000 tubes with an average length of 20 ft or more.

As time went on, technicians began using mechanical tube cleaners. There was a machine designed specifically for chillers and one designed for boilers. They consisted of a power unit that had a flexible shaft or air hose with a brush attached to it.

The results with this cleaning method were better for a number of reasons. First, the brush was spinning, which removed the build-up more efficiently than the old hand-powered method. Second, the flexible shaft could go into curves and bends, allowing for cleaning of the entire tube. And a third benefit, the process became less time- and labor-intensive.

The latest generation of tube cleaners is designed to serve double duty, cleaning chillers and boilers.

These new “dual” cleaners have a brush that spins at high rpm and provide a high volume of water for flushing the chiller tubes. This combination scrubs the inner tube walls while high-flow flushing with water loosens deposits out of the tube sheet.

Chiller manufacturers are installing enhanced tubes in today’s models that have a spiral groove or rifling inside the tube. This presents more of a cleaning challenge. Some of the latest tube cleaners have forward and reverse controls, making thorough cleaning of these grooves easier due to the absence of opposing forces. This leads to less operator fatigue.

With additional attachments, these cleaners can clean boilers, scrubbing the walls of the boiler — via the spinning brush — while the dry debris is vacuumed out.

Don't forget the ducts

When the main chiller or boiler is cleaned, the technician’s work is not finished. It is important to see the hvac equipment within a building as a whole system, rather than just focusing on one part of it.

This is especially true when cleaning is being performed.

Attention must be given to the hvac ductwork. Dirty ductwork can also rob the building of performance due to clogged filters. Sure signs of dirty ductwork are continuous repairs of mechanical systems due to reduced airflow and also high replacement costs of air filters.

These signs are usually overlooked until building owners or tenants start complaining about musty odor, sinus problems, nasal congestion, headaches, and other unusual symptoms.

This is a sign of a sick building, one with poor indoor air quality that is possibly due to a problem within the hvac ductwork. To alleviate these problems, the ductwork should be cleaned and sanitized.

There are numerous ways to clean ductwork, including hand vacuuming, high airflow vacuuming, portable duct vacuuming, and using devices that bang on the walls of the duct to loosen debris.

Vacuuming by hand is effective for shorter duct lengths, but somewhat impractical if you have to clean ductwork of 25 ft or more.

Truck-mounted or high-flow vacuums work quite well. It is important to remember that with these vacuums, the hose must be brought into the building to the area where the work is being done and may interfere with the tenants.

Portable vacuums can provide a solution to this problem. They can be transported directly to the work area with minimal obstructions and provide similar results with an air flushing unit.

Vacuuming is only one part of completely cleaning ductwork. Particles adhere to the interior walls of the duct and must be wiped off in order for the vacuum source to remove them.

There are many different devices that go into the ductwork to loosen and agitate the debris from the walls. Some technicians use air fingers, nylon wires, or tether balls to bang on the sides of the duct to loosen the debris for vacuuming.

For example, with a powered brushing system with air flushing, the brush breaks the static cling of the debris on the entire wall, while the compressed air at the brush head pushes it to the vacuum source for removal.

After the ductwork has been cleaned and vacuumed, the need for sanitizing must be considered. Some contractors sanitize all ductwork that they clean. Others don’t sanitize any of the ductwork they clean. And still others have a sanitizing protocol with guidelines for when they deem it to be necessary.

In cases of Sick Building Syndrome, especially when occupants have complained of health-related problems, it is advisable. Sanitation will virtually eliminate molds and bacteria growing within the system.

Once the section of duct is cleaned, if it is to be sanitized, the technician applies a biocide by spraying or fogging to kill any bacteria. Many contractors prefer using a low-volume fogger because it reduces the amount of water introduced into the ductwork.

Many of the problems associated with poorly performing mechanical systems and ductwork can be avoided with annual cleaning and check-ups of these systems.

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